Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

FXUS63 KLSX 091745

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1145 AM CST Mon Dec 9 2019

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 253 AM CST Mon Dec 9 2019

Regional radars and surface observation are showing showers over
the area Missouri and Illinois early this morning. These are 
occurring in an area of broad low level warm advection underneath 
a weak shortwave. The highest concentration of showers are over 
southwest/south central Illinois where the strongest low level 
moisture advection is. The shortwave will move east of the area 
this morning leaving a combination of scattered showers/light 
drizzle. However another weak shortwave currently over the Plains
will move across the region this afternoon bringing another round
scattered showers during the afternoon. Still expect the rain to 
end from west to east late this afternoon into the early evening 
as the shortwave moves quickly off to the east and drier air moves
into the region through a deep layer of the atmosphere. Tuesday 
is still expected to be dry as the NAM/GFS shows surface high 
pressure moving into the area.

Temperatures currently are in the upper 40s and highs will climb 
into the 50s before a cold front moves southeast across the region
around midday. Temperatures in the northern and western CWA will 
fall this afternoon behind the front. Highs on Tuesday will be 
below normal with the cold air advection.


.LONG TERM...  (Tuesday Night through Sunday)
Issued at 253 AM CST Mon Dec 9 2019

Both the GEFS and the ECMWF EPS are in decent agreement that the 
area will remain dry mid to late week as an upper trough moves 
off to the east with upper flow will become zonal across the 
Midwest. There will be another chance of rain/snow by next weekend
as the next upper trough drops into the Upper Midwest. 

The aforementioned surface high will move across the Midwest at 
the same time with near normal temperatures expected on Wednesday 
on Thursday. Temperatures are expected to climb a bit above normal
on Friday and Saturday as the mean low level flow turns out of 
the southwest ahead of the next front which is forecast to move 
through on Saturday. Temperatures will fall at or just below 
normal on Sunday behind the front.



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1131 AM CST Mon Dec 9 2019

The cold front has just passed through KCOU and KUIN and is
forecast to move through the metro terminals by mid afternoon.
Patchy drizzle or a few showers are possible over the next few
hours, but the rest of the afternoon through the remainder of the
TAF period will be dry. Ceilings will improve a few hours after
the front, but low MVFR conditions should dominate this afternoon,
with a brief period of IFR ceilings are expected. The other 
significant change with frontal passage will be the winds. Look 
for a sharp veering from the southwest to the northwest along with
gusts increasing to 25-30 mph. These gusty northwest winds will 
continue tonight and slowly subside toward Tuesday morning. 
Ceilings should improve several hours after frontal passage, with 
only mid or high-level clouds expected tonight and Tuesday 


The cold front is expected to pass through the terminal around
2100 UTC. Ahead of it, southwest winds along with low MVFR
ceilings are expected along with the possibility of patchy
drizzle. A brief period of IFR ceilings are also possible early
this afternoon. Behind the front, gusty northwest winds on the
order of 25-30 mph are expected. By early evening, ceilings are
forecast to rise to VFR levels and remain that way through the day
on Tuesday. 




National Weather Service Glossary of Abbreviations